Today's wireless telecommunications networks provide telephone subscribers with the ability to access telecommunications services from almost anywhere in the world. The key to facilitating such world-wide access is mobility management. With mobility management, wireless networks are able to track the location of mobile stations so that mobile services can be delivered to them.
A wireless network is typically formed of a number of cells, each covering a small geographic area within which a mobile device, such as a mobile station, may receive mobile services. Each cell is equipped with a base station that provides radio coverage to the cell, thereby enabling communication with mobile devices located within the cell. By integrating the coverage of multiple base stations, a wireless network is able to provide radio coverage to mobile stations over a large geographic area.
The coverage area of a collection of neighboring base stations is commonly referred to as a location area. Each location area is served by a mobile switching center (MSC), and each MSC may serve multiple location areas. The MSC is the network node that provides circuit-switched calling, mobility management and other telecommunications/mobile services to mobile subscribers. In particular, the MSC maintains subscriber data for all mobile subscribers that are currently located within one of the location areas served by the MSC. Mobile subscriber data is permanently maintained in a home location register (HLR) within the wireless network. When the mobile station is within the range of an MSC, that MSC acquires a copy of the mobile subscriber data from the HLR and maintains it in a visiting location register (VLR). The location area of the mobile station is also maintained in the visiting location register (VLR) for the MSC to page the mobile station in the location area for a mobile termination call. An MSC that is associated with the current location area of a mobile station is referred to as a visiting mobile switching center (VMSC) relative to the mobile station. The MSC receiving a call that is intended for the mobile subscriber is referred to as a Gateway MSC.
When a mobile station moves or “roams” into a new location area, the mobile station must inform the wireless network of the change in location area by performing what is commonly referred to as a location update procedure. Each mobile device is responsible for comparing the stored LAI (location area id) with the LAI of the newly selected cell. If the mobile device finds that the received LAI is different from the stored LAI, the mobile device sends a location update request to the wireless network. If the new location is served by a different VMSC than the previous location area, an inter-VLR location update is performed.
During the inter-VLR location update, the new VMSC that receives the location update request from the mobile station transmits an update location message to the HLR of the mobile subscriber. Upon receiving the update location message, the HLR forwards the subscriber data associated with the mobile subscriber to the new VMSC for temporary storage in the VLR of the new VMSC and updates its records to indicate that the mobile station is now served by the new VMSC. In addition, the HLR sends a message to the old VMSC to delete its subscriber record for this mobile subscriber since the mobile station is no longer served by the old VMSC.
Once the location update procedure is complete, the mobile station stores the new LAI and can continue to receive mobile services through the new VMSC. For example, in a typical mobile terminated call scenario, an incoming call to the mobile station is first routed to a gateway mobile switching center (GMSC) of the called mobile station's HPLMN (Home Public Line Mobile Network). Upon receiving the call, the GMSC queries the HLR of the mobile subscriber to determine the VMSC on which the mobile station is currently registered. The HLR typically obtains routing information from the VMSC and returns it to the GMSC. The GMSC uses the routing information to route the call to the VMSC. The VMSC accesses its subscriber data for the called mobile subscriber to determine its location area and pages the mobile station within that location area to set-up a call connection between the caller and the mobile subscriber.
However, if the mobile terminated call is received during the time that the mobile station is performing an inter-VLR location update, the mobile terminated call may not be completed to the mobile station. For example, if the HLR has not yet been informed of the change in VMSC when the GMSC queries the HLR for routing information, the HLR will return the routing information for the old VMSC to the GMSC. Thus, the GMSC will route the call to the old VMSC which will attempt to page the mobile station. Since the mobile station is no longer in the VMSC location area, the mobile device will not be able to answer the page. Currently, when a mobile device does not answer a page for a mobile terminated call, the VMSC requests the GMSC to reroute the call to the new VMSC. This mechanism is called Mobile Termination Roaming Retry (MTRR) and is further described in WO 2008/033951, Delivery of Mobile Terminated Call During Inter-VLR Location Update, incorporated by reference. This is dissatisfactory for many mobile subscribers and network providers since two potentially international calls must be placed serially from the GMSC to a VMSC. This can introduce substantial delay in call setup while wasting network resources during establishment of the first call.
Therefore, what is needed is an improved mechanism for delivering mobile terminated calls to mobile stations during inter-VLR location updates.